Inches of water to centimeters of mercury conversion calculator above calculates how many centimeters of mercury are in 'X' inches of water (where 'X' is the number of inches of water to convert to centimeters of mercury). In order to convert a value from inches of water to centimeters of mercury (from inH2O to cmHg) just type the number of inH2O to be converted to cmHg and then click on the 'convert' button.